Add context done case to waitForEvent

If the context is done before all the tasks are read from the queue,
the remaining tasks on the queue will not be read and so the done
channel will not be closed causing the goroutine to wait forever.

This is solved by adding a context.Done() check so that when the
context is closed we can carry on with shutting down of the iteration.

browser/browser_context_mapping.go

@@ -1,6 +1,7 @@
 package browser
 
 import (
+	"errors"
 	"fmt"
 	"reflect"
 
@@ -126,7 +127,12 @@ func mapBrowserContext(vu moduleVU, bc *common.BrowserContext) mapping { //nolin
 							close(c)
 							return nil
 						})
-						<-c
+
+						select {
+						case <-c:
+						case <-ctx.Done():
+							err = errors.New("iteration ended before waitForEvent completed")
+						}
 
 						return rtn, err //nolint:wrapcheck
 					}